(a) Field of the Invention
The present invention relates to an apparatus of driving a light source for a display device.
(b) Description of the Related Art
Display devices used for monitors of computers and television sets include self-emitting displays such as light emitting diodes (LEDs), electroluminescences (ELs), vacuum fluorescent displays (VFDs), field emission displays (FEDs) and plasma panel displays (PDPs) and non-emitting displays such liquid crystal displays (LCDs) requiring light source.
An LCD includes two panels provided with field-generating electrodes and a liquid crystal (LC) layer with dielectric anisotropy interposed therebetween. The field-generating electrodes supplied with electric voltages generate electric field in the liquid crystal layer, and the transmittance of light passing through the panels varies depending on the strength of the applied field, which can be controlled by the applied voltages. Accordingly, desired images are obtained by adjusting the applied voltages.
The light may be emitted from a light source equipped in the LCD or may be natural light. When using the equipped light source, the total brightness of the LCD screen is usually adjusted by regulating the ratio of on and off times of the light source or regulating the current through the light source.
A lighting device for an LCD, i.e., a backlight unit includes a light source and an inverter for driving the light source.
The light source typically includes a fluorescent lamp and the inverter converts an input DC (direct current) voltage into an AC (alternating current) voltage and applies the AC voltage to the lamp.
The backlight unit is classified into a backlighting type and an edge lighting type depending on the packaging configuration of mounting the lamps. The backlighting type configures the lamps directly behind the panels, and normally includes several lamps.
When using several lamps, the brightness of the each lamp needs to be kept uniform, and thus the current flowing through each lamp always needs to be maintained constant. For this purpose, a current sensor for detecting the current of the lamp is installed at each lamp and the amount of the current in each lamp is controlled based on the detected current.
When feedback-controlling the operations of the lamps in independent manner, separate wires for connecting the respective lamps to the inverter are required. Accordingly, the productivity is reduced since the circuit design for an inverter may consider several wires, and the feedback-control of the lamps may become inexact due to the increased noise and interference between the wires.
For solving these problems, it is suggested that all the lamps are connected to the inverter by a single line and the control of the lamps are based on the current in the single line.
However, this method cannot separately control the lamps since the state of each lamp cannot be distinguished. For example, when one of the lamps is out of order and the current therein does not flow or decreases, it cannot be determined whether the lamp is out of order since the total current flowing through the entire lamps, which is detected to be decreased, does not tell the state of each lamp. In this case, the feedback control increases the total current in the entire lamps, and then the defected lamp, which cannot capable of performing normal lighting operations, is also supplied with current or voltage. The continuous application of the voltage to the defected lamp may result in arcs or spikes, which exerts a bad influence on the lamp and the entire backlight unit as well.